Control circuit



April 23, 1963 H. G. KEOGH, JR 3,087,066

CONTROL CIRCUIT Filed Oct. 24, 1960 =F-L5O UTILIZATION FlG. I DEVICE .59 g ----REI AY PULL IN .Jl- A "6 -RELAY DROP OUT l" AI FIG. 2 62 so LIGHT INTENSITY I I 39 I2 as 46 I0 INVENTOR FIG. 3 HOWARD s. EOGH, Jr

ATTORNEY United States Patent 3,087,066 I CONTROL CIRCUIT Howard G. Keogh, Jr.,.Poughkecpsie, N.Y., assignor, by mesne assignments, to Daystrom, Incorporated, Murray Hill, N.J., a corporation of Texas Filed Oct. 24, 1960, Ser. No. 64,452

. 7 Claims. (Cl. 250206) This invention relates to a radiation responsive control circuit and, more particularly, in a preferred embodiment of this invention, toa self-saturating magnetic amplifier controlled in response. tothe. intensity of radiated light.-

Many control systems have been developed in the past using DArsonval microampers movements in conjunction with an optical feedback system incorporating photosensitive elements. 7

Thesepriorart systems include contactless type of indicating controls utilizing a vane attached to the pointer of a microamperecmovernentfl This vane passes in the path-of a light beam to block the'light from a detectingphotocell. The action of the photocell actuates a. sen.sitive relay which in turn operates through a secondary control element such as a power relay to control; for example, the heat applied to afurnace.

. Many-con'trol circuitsrhave been developed which are capable of detecting the vane movement, or position. One such circuitisdescribed in United States Patent No. 2,892,092, issued June 23; 1959., to Joseph L. Behr. The Behrrpatent describes a light-responsive self-saturating magnetioarnplifier wherein the light-sensitive element, instead of being in circuit with a separate control winding, is connected in a current path which shunts the saturating rectifier and supplies the reactor power winding with: desaturating current... Also in the Behr circuit, the resistance .of..the.light-sensitive element is employed to control :the desaturating current :and consequently the output of the amplifier.

-Such control systems find use in various industrial processes wherein physical conditions, such as tempera ture,-- percentage of hydrogen ion concentration, voltage, orcurrent have'to be maintained constant or limited to specific values. .These prior art circuits have many advantages; but unfortunately, also have certain disadvantages. Because of the nature of the process involved, any automatic control circuit used, desirably should perform with the highest degree of reliability,'sensitivity and stability over relatively long periodsof time.

Among the disadvantages of the prior art circuits are the unwanted relay chatter due to the relay contacts failing to achieve a firm make or break con-tact. Also, the speed of response of these prior circuits was often so fast that ittended to cause unwanted relay action due to vibration of the pointer and vane of the meter movement. Also," in order to achieve a stable operation, there was a certain amount of dependency upon the line voltage. To prevent this,'someof these prior circuits required relatively expensive relays having a small pull-in to dropout ratio as well as relatively high quality magnetic cores. Both of these requirements often led to costlier units than is desired.

It is, therefore, an object of'this invention to overcome many of the disadvantages of the prior art control circuits.

Another object of this invention is to accurately control an output relay in response to light.

In accordance with the present invention, an improved light-responsive, self-saturating magnetic amplifier has a light-sensitive element connected in a current path that shunts the saturating rectifier and supplies the main reactor winding with desaturating current. The light-rea hysteresis type actioncf sponsive resistance of the light-sensitive element is employed to control the desaturating current and hence, the output of the amplifier. The output of the amplifier is the voltage developed. across the main reactor winding, and hence, approaches zero when the reactor is saturated; and, conversely, approaches line voltage when the reactor is desaturated (in the presence of light).

In one embodiment of the invention, to improve the amplifier response, a serially connected feedback winding on the reactor and a unidirectional conducting device are connected in shunt with the main reactor winding. The feedback winding is paralleled by a storage capacitor to store the voltage developed across the main reactor winding. The winding of an output relay is serially connected to the feedback winding.

The action of the feedback winding is such as to cause the control circuit. With an increase in light applied to the light-sensitive device, some point is reached at which the relay is actuated. On the other hand, as the light is decreased, the relay does not drop out with the same amount of light with which it was actuated. Instead, the light intensity must decrease below the intensity at which the relay originally was actuated in order to cause a relay to again'drop out.

This hysteresis action improves the stability of the control circuit for line voltages and insures snap action of the output relay.

Further advantages and features of this invention will become apparent upon consideration of the following description read in conjunction with the drawing wherem:

FIGURE 1 is a circuit diagram of light-responsive control circuit utilizing a self-saturating magnetic amplifier in accordance with oneembodiment of this invention;

FIGURE 2 is a graph of the control voltage, developed from the control circuit illustrated in FIGURE 1, plotted as the ordinate versus the light intensity applied to the light-sensitive device in the control circuit pl'otted as the abscissa; and

FIGURE 3 is a circuit diagram of a light-responsive control circuit utilizing a self-saturating magnetic amplifier in accordance with another embodimentof this invention.

The term self-saturating magnetic amplifier has an accepted meaning in the art and refers to a circuit in which the main reactor winding of a saturable cone reactor is always in-series with a switching device having recurring active and inactive periods. The switching device, which may be, for example, a unilateral conducting device, allows periodic, unidirectional, current pulses to flow in the main reactor winding during the conductive or active periods of the switching device and little or no current to fiow therein during the inactive periods of the switching device. Hence, the reactor is driven into magnetic saturation during the active periods of the switching device. This magnetic saturation ismost commonly known as self-saturation.

Hereinafter, current flowing through the main reactor winding in the direction which provides or aids the magnctization will be referred to as saturating current, and the direction of such flow shall be referred to as the saturating direction. On the other hand, current which flows through the main reactor winding in a direction to oppose the magnetization will be referred to as desaturating current; and the direction of its flow, the desaturating direction. The cyclic switching device, whether it be an asymmetric conductor, mechanical means or other, may be referred to as the unilateral conducting device, or diode, because it provides the pulsed unidirectional current for self-saturation.

In the amplifier illustrated in FIG. 1 are included a pair of power input terminals which are coupled to the primary winding 12 of a transformer 14 having a step-down secondary 16- and an output secondary winding 18. The input terminals 10 may be connected to a source of alternating current power supplying, for example, 117 volts at 60 cycles. The magnetic amplifier illustrated in FIG. 1 also has a pair of output terminals 20 across which may be connected the winding 22 of a control relay 24 which closes a pair of control contacts 26. Connected between the input terminals 10 and the output terminals 20 is the magnetic amplifier constructed in accordance with this invention.

The magnetic amplifier includes a main reactor, or power winding 36, on a saturable core reactor 38, connected in series with a unilateral conducting device 40, and also, a light-sensitive device 42. The unilateral conducting device 40 and the photocell 42 are connected in parallel with each other in a circuit between the secondary 18 of the transformer 14, which provides the input to the magnetic amplifier through a current limiting resistor 44, and the output circuit 43 of the amplifier. The output circuit 43 is connected across the power winding 36, i.e., between the output terminals 20 and the junction 47 between the diode 40 and the power winding 36.

The output circuit 43 includes a feedback winding 46 on the saturable reactor 38 that is connected in series with a second unilateral conducting device 47, which also may be a diode or mechanical switch. Shunted immediately across the feedback winding 46 is a resistor 48 which may be adjustable. Connected in parallel with the series combination of the feedback winding 46 and the output terminals 20 (relay winding 22) is a storage capacitor 50. Thus, the voltage developed in the output circuit 43 of the magnetic amplifier is dependent upon the impedance presented by the power winding 66 to the input voltage derived from the secondary winding =1 8.

The unidirectional conducting devices 40 and 47 are poled in the same direction and may be any suitable device; such as, a silicon diode that is capable of allowing current flow substantially in one direction only. The light-sensitive device 42 may be of any type whose resistivity is responsive to the intensity or the wave length or both of light radiation. A photocell, for example, employing a light-sensitive material such as cadmium selenide or other well-known materials whose resistivity changes in response to light is suitable. The term light is employed herein in its broadest sense to include all forms of detectable radiation. Characteristics and structural details of light-sensitive cells of various types are well-known and a further description thereof is believed unnecessary.

The resistance of a light-sensitive element, such as the device 42, usually varies from a high to a low value as the intensity of light is increased from a low to a high value or as a particular wave length to which the cell is most responsive is approached. For purposes of illustration, the present magnetic amplifier is illustrated in a pyromillivoltmeter type circuit in which a vane 52 is attached to the needle (not shown) of a DArsonval type meter movement and so positioned as to be interposed in the light path between a source of light 54 and the light-sensitive element 42. The light source 54 may, for example, be an incandescent lamp energized by the secondary 16 of the transformer 14. Both the light-sensitive device 42 and the light source 54 may be enclosed by a light-proof enclosure (not shown) to prevent extraneous light from affecting the light-sensitive element 42.

The operation of the control circuit of this invention may be explained as follows. When the controlled variable, for example, the temperature of an electric furnace, which may be controlled by the opening or closure of the relay contacts 26, is below some predetermined set point, as is determined by the physical position of the vane 52 with respect to the light source 54 and photocell 42, the vane 52 allows light from the light source 54 to fall on the photocell 42. The resistance of the photocell 42 drops to a lower value. Therefore, on the negative going, or reset half-cycle portion of the alternating current signal'derived from the source 10, desaturating current flows through the the saturable reactor 38 desaturates. The reactor 38 is now said to be reset.

Thus reset, the saturable reactor 38 presents a relatively high impedance to the flow of saturating current through the power winding 36 during the positive-going portion of the input voltage- Saturating current passing in the forward conducting diode 40 develops a voltage across the power winding 36. This voltage also appears across the output circuit '43. This voltage, which is transmitted through the sec ond diode 47 to the storage capacitor 50 and the feedback winding 46 each reset half-cycle, increases in the voltage developed across the capacitor and the output terminals 20. Discharge current from the capacitor 50 during each reset half-cycle passes through the feedback winding 46 due to the blocking action of the second diode 47. This discharge current is in such direction as to aid in desaturating or resetting point is finally reached of which the two resetting currents, i.e., that in the power winding 36 and that in the feedback winding 46 are sufiicient to develop enough voltage across the power winding 36 during the positivegoing half-cycle such that the relay 24 pulls in and closes the contacts 26. In the assumed illustration, the closure of the contacts 26 causes more heat to be applied to the furnace.

Now, as the temperature of the furance increases and the vane 52 again starts to cover the photocell and block the flow of light thereto, the resistance of the photocell 42 increases. This increase in resistance decreases the reset, or desaturating, current that flows through the power winding 36. The discharge current from the storage capacitor 50, however, continues to flow for several cycles, during the reset half-cycle, in such a direction as to desaturate the saturable reactor 38. The saturable reactor 38, therefore, is prevented for a short period of time from becoming saturated during each positive half-cycle of the power supply voltage. A point is finally reached at which the discharge current from the capacitor is insufiicient to prevent saturation of the saturable reactor 38 and the voltage developed across the power winding 36 in sufficient to maintain the relay 24 actuated. Hence, the relay 24 drops out, disengaging the contacts 26.

It may be pointed out that due to the unique feedback circuit of this invention, a differential exists between the relay pull-in and drop-out points. That is, although the relay pulls-in, as illustrated in the graph of FIG. 2 by the rapid increase in relay voltage to the point 59 with a certain amount of light, illustrated by the point 60, impinging on the photocell 42, once pulled in,. the relay 24 resists dropping out until a lesser amount of light is present on the photocell 42. This lesser amount of light is illustrated by the point 62 in FIG. 2, which it may be noted is to the left of (closer to zero light intensity) the pull-in point 60.

This difference between the relay pull-in and drop-out points 60 and 62, respectively, may be termed a hysteresis type action which aids in giving the magnetic amplifier a more positive, or snap-type action, that is relatively insensitive to line voltage variations or extraneous light variations such as might be caused by vibration of the vane 52. The amount of hysteresis may be adjusted by varying the resistor 48 or the capacitor 50.

As a result of this nvention, a relatively inexpensive relay 24 may be employed due to the snap-action" provided by the feedback circuit. In addition, the material photocell 42 and I direction through the first the saturable reactor 38. A

selected for the saturablefreactor 38 may be of lower quality as it is -not required to have a substantially rectangular hysteresis 'loop as was often required in the prior art. '.=Also, the circuit of FIG. 1 is fail-safe in that, in the event of power failure, the relay drops out.

The circuit. of FIG 3 illustrates an alternative embodiment of this invention in which the feedback or output circuit 43 is connected in series with the power winding 36 of the magnetic amplifier rather than in parallel as illustrated in FIG. 1. Since the elements. of FIG. 3 are, for the most part, identical to thoseemployed by FIG. 1 ,,-the,same reference numerals have been employed. The primary difference between these a two embodiments is thatin FIG. .3.the'relay winding 22 of the relay. 24 replaces the. resistor 44 (FIG. 1) and is connected in series with the power winding 36. The feedback winding 46' is connected in-shunt withthe relay winding 22 through the storage capacitor 50. The feedback winding 46 is shunted by the adjustable resistor 48 as before. The relay contacts 26 (FIG. 1) are not shown in FIG. 3. The remaining circuit connections in the embodiment of. FIG. 2 are the same as in FIG. 1, and accordingly no further description herein will be made.

The operation of the embodiment of FIG. 3 is substantially the same as that of FIG. 1 except that its re sponse to light is the opposite. Initially, in the presence of light, such as caused by the vane 52 allowing light to fall on the photocell 42, equal saturating and desaturating currents flow through the power winding 36 during each half-cycle of the power supply voltage. Hence, the reactor 38 is not saturated and the power winding 36 presents a high impedance to the current flow. The resulting decreased current flow through the relay winding 22 is insuificient to pull-in the relay 24. Now, as the vane 52 moves between the light source 54 and the photocell 42, the amount of light falling on the photocell 42 decreases, thereby decreasing the desaturating current in the power winding 36. The reactor 38 begins to saturate resulting in an increased voltage drop across the relay winding 22. The capacitor 50 charges through the feedback winding 46 in such a direction as to oppose the saturating current and aid the desaturating current (which is now decreasing in magnitude). This feedback action delays the saturation of the reactor 38 until the light intensity of the photocell 42 decreases still further. After several cycles of the input alternating current from the source 10, in the presence of decreasing light intensity, the reactor 38 gradually is driven to saturation due to the decreased desaturating current. When the light intensity decreases to a predetermined value, the saturating current flow is sufiicient to pull-in the relay 24 and close the contacts 26 (not shown).

With the reactor 38 saturated, the majority of the voltage drop occurs across the relay winding 22 instead of the power winding 36. The capacitor 50 stores this voltage such as to maintain the relay winding 22 energized during the desaturating portion of the cycle (there is little or no current How to the power winding 36 since the photocell 42 is a high impedance).

Conversely, with an increase in light intensity on the photocell 42, the reactor 38 begins to desaturate. With desaturation of the reactor 38, the magnitude of the saturating current decreases due to the higher impedance of the power winding 36. The resulting decreased voltage drop across the relay Winding 22 causes a discharge current from the capacitor 50 which passes through the feedback winding 46 in such a direction as to aid the saturating current in saturating the reactor 38 and to oppose the desaturating current. The action is cumulative and the reactor 38 quickly desaturates such that the power winding '36 again presents a relatively high impedance. With the resulting reduced current flow through the re lay winding 22, relay 24 drops out.

The functioning of the feedback winding 46, which aids and opposes saturating and desaturating, respectively,

the reactor 38 of the magnetic amplifier, causes the hysteresis type action. similar to that described in the embodiment 'of FIG. 1.. This hysteresisia'ction results in the relay 24 dropping out with a greater light intensity impinging on the photocell 42 than is required to cause the relay 24 to again pull-in with decreasing light inteny- 7 There has thus been described a relatively simple control circuit using a light-responsive, self-saturating type magnetic amplifier having hysteresis type action. The hysteresis action provides a snapaction typeof output and allows the use of less expensive output relays. Fur ther, the circuit may be adjusted such that it is relatively insensitive to line voltage variations or extraneous vibrations; for example, of the vane attached'to a DArsonval type meter movement. Further, in one of the embodiments of this invention, the circuit is fail-safe; inthe event of power failure, the relay drops-out.

Since many changes could be made in the above construction and many apparently widely differentembodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a self-saturating magnetic amplifier including a reactor with a magnetically saturable core having a power winding and a feedback winding on said core, unidirectional conducting means connected in series with said power Winding for passing intermittent unidirectional current through said power winding in a particular direction thereby to saturate said core, means having light-responsive conductivity connected in series with said power Winding and etfectively in shunt with said unidirectional conducting means for creating a voltage drop across said power winding in response to light, the combination comprising capacitance means and a second unidirectional conducting means connected in series with each other and in parallel with said power Winding, said feedback winding being connected in parallel with said capacitance means whereby the voltage developed across said capacitance means changes differentially with increasing or decreasing light and said amplifier provides a hysteresis type response to light impinging on said light responsive means.

2. A self-saturating magnetic amplifier comprising a reactor with a saturable core having a power winding and a feedback winding on said core, a source of current alternatively having a first polarity and a second polarity, first means connecting said current source to said power winding for allowing current of one of said polarities to flow through said power winding in a direction to saturate said core, second means coupled between said current source and said power Winding for selective passing current of said second polarity through said power winding in a direction to re duce the saturation of said core, and storage means connected in parallel across said power winding for storing the voltage of said one polarity developed across said power Winding when said core is unsaturated, said feedback winding being coupled across said storage means for opposing the saturation of said core and aiding the desaturation of said core, thereby to provide a rapid differential response to variations of said second means.

3. A self-saturating magnetic amplifier comprising a reactor with a saturable core having a power winding and a feedback winding on said core, means connected in series with said power winding for passing intermittent unidirectional current through said power winding in a particular direction, means having light-responsive con ductivity connected in series with said power winding and effectively in shunt with said unidirectional current means for passing current through said power winding in the opposite direction in response to light, an output circuit 7 connected in series with said power winding, and a capacitor, said capacitor and said feedback winding being connected in series with each other and in parallel with said output circuit, thereby to provide a differential response to increasing and decreasing amounts of light.

4. A self-saturating magnetic amplifier as set forth in claim 3 wherein a variable resistor is coupled in parallel with said feedback winding thereby to control the amount of differential response of said amplifier.

5. A self-saturating magnetic amplifier comprising a reactor with a saturable core having a power winding and a feedback winding on said core, means connected in series with said power winding for passing intermittent unidirectional current through said power winding in a particular direction, means having light responsive conductivity connected in series with said power winding and effectively in shunt with said unidirectional current means for passing current through said power winding in direction opposite said particular direction in response to light, and a second means connected in parallel with said power winding for passing intermittent unidirectional current,

and capacitance means connected in series with said second unidirectional current means, said feedback winding being connected in parallel with said capacitance means and in series with said second unidirectional current means.

6. The combination set forth in claim 5 which also includes an impedance means connected in parallel with said feedback winding.

7. The combination set forth in claim 6 which also includes an output circuit connected in series with said feedback winding whereby the current supplied to said output circuit varies difierentiallyin response to increasing and decreasing light intensity impinging on said light responsive means and hence is less sensitive to the re ceipt of undesired variations of said light intensity.

Behr June 23, 1959 Brown May 23, 1961 

1. IN A SELF-SATURATING MAGNETIC AMPLIFIER INCLUDING A REACTOR WITH A MAGNETICALLY SATURABLE CORE HAVING A POWER WINDING AND A FEEDBACK WINDING ON SAID CORE, UNIDIRECTIONAL CONDUCTING MEANS CONNECTED IN SERIES WITH SAID POWER WINDING FOR PASSING INTERMITTENT UNIDIRECTIONAL CURRENT THROUGH SAID POWER WINDING IN A PARTICULAR DIRECTION THEREBY TO SATURATE SAID CORE, MEANS HAVING LIGHT-RESPONSIVE CONDUCTIVITY CONNECTED IN SERIES WITH SAID POWER WINDING AND EFFECTIVELY IN SHUNT WITH SAID UNIDIRECTIONAL CONDUCTING MEANS FOR CREATING A VOLTAGE DROP ACROSS SAID POWER WINDING IN RESPONSE TO LIGHT, THE COMBINATION COMPRISING CAPACITANCE MEANS AND A SECOND UNIDIRECTIONAL CONDUCTING MEANS CONNECTED IN SERIES WITH EACH OTHER AND IN PARALLEL WITH SAID POWER WINDING, SAID FEEDBACK WINDING BEING CONNECTED IN PARALLEL WITH SAID CAPACITANCE MEANS CHANGES DIFFERENTIALLY WITH INCREASING OR DECREASING LIGHT AND SAID AMPLIFIER PROVIDES A HYSTERESIS TYPE RESPONSE TO LIGHT IMPINGING ON SAID LIGHT RESPONSIVE MEANS. 